KokaKona wrote:I use all the slightly unscientific ways mentioned of trying to guess the health of my harvested cells, but I was wondering what equipment you'd recommend Archie to do the job properly? Is it expensive, because if so I guess it goes against the grain of getting the cells for free in the first place? I wondered for example whether there was some cheap PC software/hardware which could charge-discharge and record data...
Well, sometimes it's wise to invest initially, to save later.
The cell's state is determined by such major parameters as capacity, internal resistance, and self-discharge rate. Most important is, obviously, first one. It's very convenient to measure it by using processor-based universal charger, widely available as "hobby charger": I personally use Turnigy AccuCell 6
. It is equipped with RS232-TTL data port (serial output), providing connection to PC via appropriate adapter: typically to USB. I've connected Bluetooth transmitter to it, so it transfers measurement data wirelessly. To collect & analyze the data, I use freeware LogView
software, powerful and highly configurable, exporting results to the Excel spreadsheet and pictures with charge/discharge curves. It requires also separate power supply (charger itself capable to provide 6A current, but for playing with 18650, less expensive 2A supply is enough), adapter(s) for battery connection, and optionally thermal sensor.
Please note that sometimes such chargers are not calibrated properly at the factory, so it's worth checking/adjusting by external voltage reference.
For resistance measurement, I use Sinometer SM8124
impedance meter, but it requires a bit of modding. Device itself is very good, with proper four-wire Kelvin scheme, but is supplied with ordinary DMM-style test leads where cables are internally shorted together, spoiling whole purpose of using it. You'll have to buy correct Kelvin probes, or make ones yourself. I prefer the latter method, and used spring-loaded gold micro test pins and holders to make them.
As for self-discharge, I use Victor 86B
meter with optical RS232 interface and USB receiver: supplied "DMM Data Processor" software collects the data, and is also capable of exporting directly into Excel spreadsheet.
On the photo below, you can see one of my self-made high capacity 12-cell 6P2S battery assembled with 18650 cells extracted from discarded notebook batteries and matched by parameters, using mentioned apparatus.
This particular set of equipment, of course, is just my personal setup: you can choose any other pieces more appropriate for your requirements. For beginning, hobby charger alone is probably sufficient. Good luck!